1. Field of the Invention
The present invention relates to a semiconductor switch apparatus used to drive a vehicle starter.
2. Background Art
An electromagnetic switch having mechanical contacts has been used to drive a vehicle starter. As is shown, for example, in JP-A-2009-224315, a main switch to drive a starter is formed of a solenoid incorporating a switch coil and a plunger and configured to operate as follows. That is, as the switch coil is energized, an electromagnet is formed for the switch coil to attract the plunger and a main contact is closed in association with motion of the plunger. When energization of the switch coil is stopped and the attraction force vanishes, the plunger is pushed back by a reaction force of a spring and the main contact is opened.
In order to meet the demand for low fuel-consumption and low emission in recent years, an idling stop and start system that automatically stops the engine when the vehicle stops running and restarts the engine when the vehicle starts running again is put into practical use. In the idling stop and start system, because the engine is started each time the vehicle stops and starts running again, the engine is started far more frequently than in an engine control system in the related art.
The electromagnetic switch having mechanical contacts in the related art therefore has a problem that durability is not satisfactory. Also, in the event of failure, such as contact fixation, the electromagnetic switch having mechanical contacts is locked at the closing position, which raises a problem that energization of the starter cannot be stopped. Conversely, in the event of failure, such as disconnection of the electromagnetic coil, the electromagnetic switch having mechanical contacts is locked at the opening position, which raises a problem that the engine cannot be restarted.